When first completed, many gas wells have sufficient reservoir pressure to flow formation fluids to the surface along with the produced gas. As gas production continues, the reservoir pressure declines, and as pressure declines, the velocity of the fluid in the well tubing decreases. Eventually, the gas velocity up the production tubing is no longer sufficient to lift liquid droplets to the surface. Liquids may then accumulate in the tubing, creating additional pressure drop, slowing gas velocity, and raising pressure in the reservoir surrounding the well perforations and inside the casing. As the bottom well pressure approaches reservoir shut-in pressure, gas flow may stop and liquids can accumulate at the bottom of the tubing.
At different stages in the life of a gas well, various means can be employed to move accumulated liquids to the surface. These may include foaming agents or surfactants, velocity tubing, plunger lift, and downhole pumps. The proper application of pumps can lower the abandonment pressure of wells, increasing reserves captured per well, and reduce the number of wells required to economically deplete an asset.
Micro positive displacement pumps and solid state pumps are under consideration for field applications. Deployment of such pumps may be by commercially available wireline cable capable of transmitting about 2,500 watts or more of electricity to an AC or DC motor, or solid state device, powering the unit.
The break-strength of commercially available wireline can be on the order of about 20,000 lb for a 7/16″ cable. Additionally, manufacturers do not recommend exceeding 60% of the break-strength for a given cable. With a pump seated at 10,000 ft, with 9.0 ppg produced water, and assuming a tool having an outside diameter of about 2.5″, the total pickup weight of the entire assembly can exceed 22,000 lb, which is well in excess of the 60% working load of a 7/16″ cable. As may be appreciated, such loads could make the seating of such pumps at those depths prohibited.
Therefore, what are needed are systems and methods for reducing the force required to pull a device from a tubular.